Photographic exposure meter



. 8, 1942. H. B. AXTELL PHOTOGRAPHIC EXPOSURE METER Original Filed March22, 1937 SIC,

L an

Fig. J

' or object being photographed, and interposing diflusing means in placethereon.

Reissued Dec. 8, 1942 Re,

UNITED- STATES PATENT OFFICE PHOTOGRAPHIC EXPOSURE- METER Harold B.Axtell, Aitadena,.0alli., assignor o! one-third to William R.Litzenberg, Los Angeles, Calif.

Original No. 2,172,634, dated September 12, 1939,

Serial No. 132,342, March 22, 1937. Application for reissue August 30,1961, Serial No. 408,919%

3 Claiml. (Cl. SE23) My invention relates particularly to photo- Figure3 is a diagrammatic representation of graphic exposure meters designedto ascertain the electric circuits; and indicate the intensity of thelight condition Figure 4 is a longitudinal sectional view in connectionwith photography, whereby the through Fig. 1 on line 4-4; correctexposure adjustments can be made in the Figure 5 is a transversesectional view taken camera; on line 5-5 of Fig. 1;

' Among the salient objects of my invention are: Figure 6 is aperspective view of a photometer to provide in such a device a variablelight which embodying my invention; and

can be adjusted to accurately correspond with Figure 'I is a fragmentaryview, enlarged, showthe light reflected into a camera from the scene ingt light receiving mirror With the 00101 n a voltmeter or otherinstrument in the circuit Referring now in detail to the drawing, my tosuch light, with means connected'ztherewith invention as here embodiedfor descriptive purfor indicating the light intensity or condition;poses consists of a box or case 3, of suitable mato provide incombination with a device oi! the m terial, having abuse 0 bo 2, Seemedin Place character referred'to, a color filter or tint sheet by Screws Alens 5 is mounted in one end for the light reflected into the camerafrom the of the case, as shown, and a ey p O lens 5 object or scenebeing photographed, and also tor is mounted in the top, as indicated. Amirror I the variable light, whereby to facilitate the adis mountedtherein, at an angle o receive light justment oi the variable light andits accurate l/S o the lens 5 d reflect direct t m correspondence to thereflected light from the to the eyepiece as indicated by the l t b o nscene or object being photographed; to provide lines. The mirror i issilvered or alumlnized" in a device of the character referred to amirror on its surface, as at 24, preferably on its upper for reflectingthe light received, said mirror or su e to eliminate double ec io f omthe other reflecting surface having a hole there- 9; surface 01' theglass when silvered on the bottom. through and having the variable lightpositioned Sa mirror provided With a hole aperture to show its lightthrough said hole to mingle 8 in the reflecting surface, which may bereferred with the reflected light rays to greatly facilitate. o as the PThis may be of a y s d 0 the process of adjusting the variable light tothe s e Size Shape. though it Preferably W same intensity as the lightreceived from the 39 e Bhmewhat elliptical in shape 80 85 to Presentscene or object being photographed; to provide the appearance. of around hole when viewed at in connection with such reflector and itshole, a a e of y-fi e es o e or- It between the variable light and saidhole, means S u preferably be small relative t t fi ld for diffusing thelight from the variable light being viewed. source, whereby to make ituniform and thus fl Below the mirror 1, p 9 1S removebly make itpossible to more accurately harmonize mounted in a suitable Socket Adiffusing the variable light and the light reflected into plate II isalso mounted on the under side of the apparatus from the object beingph0tothe mirror and may be of ground glass or other graphed; and, in.general, to provide an improved translucent material. A color or tintfilter or expgsure meter hi is compact, pracflcal and 4( sheet in ismounted between the mirror and said economical, and with which it ispossible to acdisc as indicated- This may be made of curately determinethe light condition or inten- 9nd gelatme' Preferably blue, or any othersuitsity, with suitable graduated or. measuring means 28 g f i the lightrays passing for registering the result either in light units or gzs igi g g i fi g i i photographic exposure units. desi e S y an s gnated II.In order to fully explain my invention, I have Light rays, as from thescene or object being shown on the accompanying sheet of drawingsphotographed are picked up by the lens 5 and one embodiment thereof, Iare reflected the mirror I through the eyenow describe. piece 6 to theeye, as indicated by the broken Fi 1 is a p v w of a instrum nt m lines.Light from the lamp 0, diifused by the b y y i ion, showing the pos t on01 member Ii, and tinted by the member ill, passes the battery: throughthe aperture I through the mirror I,

Figure 2 is a longitudinal sectional view thereand is mingled with thelight rays 23 passing to through on line 2-2 of Fig. 1; the eyepiecelens I, as will be understood from member 2 I, both of said membersbeing anchored in insulating means 20', and connected with circuitwires, as 2|, which include the lamp .9, as will be understood from thediagrammatic view in Fig. 3. A battery I! is shown to furnish thecurrent through said circuit. As said disc II is rotated by the thumb,the resistance winding I9 is varied relative to the contact member 2|.The

depressing of the disc IS with the thumb, as it is rotated, also movescontact member 2| into engagement with member 2|, as will be understoodfromFig. 4. This constitutes means for varying the current applied tothe lamp I.

Thus I have provided a variable light which can be varied to correspondin intensity to the light rays 13 coming in from the scene or objectbeing photographed. The spring 01 the member 20 is sufiicient to raisesaid disc l6 and break the contact between members 20 and 2| when thethumb is removed therefrom. This breaks the circuit to the lamp 9.

In Fig. 3, I have illustrated a voltmeter I4 interposed in the circuitto the lamp 9. This indicates variations in voltage to the lamp, underthe control of the rheostat I6. The voltage is proportional to thecurrent flowing in the lamp and consequently to the luminosity of thelamp. I'hevoltmeter may be calibrated in light values or in terms ofphotographic exposure values. ammeter, in series with the battery, lampand rheostat, can also be used if desired, as will be understood bythose versed in the art. In either case, a suppressed zero instrument ispreferable so that the needle will not leave the zero point I until thatvoltage is reached at which the lamp Just begins to give off light(above 0.8 volt for a 1.5 volt lamp). This extends the instrument rangeand is more easily read.

The use and operation of the invention as described may be brieflydescribed as follows:

The device is pointed in the general direction of the object or scene tobe photographed and the object located in the eyepiece 6, in the samemanner that a camera finder is used. The meter is moved until theopening or "spot 8 coincides with the particular object desired tophotograph. The-rheostat disc I6 is then depressed by the thumb of theright hand, and rotated until the spot 8 disappears or until it mostnearly matches or corresponds in intensity of iilumination of the lightfrom the object being photographed. When this condition is found, andbefore releasing the rheostat disc I6, the meter reading is observed.Suitable calculating tables may be provided for determining combinationsof shutter speed, diaphragm aperture, emulsion speeds, etc. from thisreading. For most motion picture work, for which the particularembodiment shown is designed, the meter may be direct reading.

Since the luminosity of the lamp is proportional to the current flowingin it, which is in turn proportional to the voltage impressed across it,the reading is entirely independent of current supply or batteryvoltage. The battery may be used as long as it will light the lamp. r

While I have shown and described somewhat in detail one practicalembodiment of my invention, I am aware that many changes in details ofconstruction and arrangement canbe' made therein without departing fromthe spirit of the invention, and I do not, therefore, limit theinvention to the showing made for explanatory purposes, except as I maybe limited by the hereto' appended claims.

.- I claim: I

l. A photographic exposure. meter including a housing having a lens toreceive light rays from the outside and an eyepiece to receive themtherefrom, an angularly disposed reflecting surface interposed in saidhousing to receive and reflect said light rays from said lens to saideyepiece, said reflecting suriace having an opening therethrough, anelectric lamp positioned to be seen through said opening, means fordiffusing the light from said lamp to uniformity for comparativepurposes, a variable resistance to vary the current in said electriclamp for producing an intensity corresponding to that of the lightthrough said lens, means for giving the same color -or tint to the lightrays and said electric light to harmonize them more readily, and anelectrical measuring instrument. connected to the electric lamp andcalibrated to indicate the volt age on said lamp directly in terms oflight values.

2. A photographic exposure meter including a housing having a lens toreceive light rays from the outside and an eyepiece to receive themtherefrom, an angularly disposed reflecting surface interposed in saidhousing to receive and reflect'said light rays from said lens to saideyepiece, said reflecting surface having an opening therethrough, anelectric lamp positioned to be seen through said opening, means fordiffusing the light from said lamp to uniformity for comparativepurposes, a variable resistance to vary the current in said electriclamp for producing an intensity corresponding to that of the lightthrough said lens, means for giving the same color or tint to the lightrays and said electric light to harmonize them more readily, and anelectrical measuring instrument connected in the lamp circuit forindication of light values.

3. A photographic exposure meter including a housing having an openingwith an eyepiece therefor providing a view thereinto, a second openinginto said housing with lens for admitting a view of a scene to bephotographed, and an angularly disposed reflecting surface in saidhousing, interposed between said openings to provide areflected view insaid reflecting surface of the entire scene admitted by said secondopening, said reflecting surface having an opening therein correspondingin size to a relatively small possible the matching of the lightintensity of said spot with the light intensity of said relatively smallobject in said reflected scene, and means for indicatin the degree ofintensity of the light emanating from said lamp.

HAROLD B. AXTELL.

